This invention relates to an apparatus for use during the production of multifilament, synthetic yarn. In particular it relates to a muffler, for use in conjunction with an aspirator, which reduces by up to 22.5 .DELTA. dB(A) the noise emitted at the inlet end of the aspirator when the aspirator is operational, with substantially no loss in yarn tension.
Throughout the present specification and claims, the term "dB(A)" (decibels -- A-weighted) connotes a unit of measurement of sound level corrected to the A-weighted scale, as defined in ANSI S1.4- 1971, using a reference level of 20 micropascals (2.times. 10.sup.-.sup.5 Newtons per square meter). The term ".DELTA. dB(A)" refers to the difference between two noise levels where each level is expressed in units of dB(A). The term "yarn" is employed in a general sense to indicate strand material, either textile or otherwise, and including a continuous, often plied, strand composed of fibers, filaments, glass, metal, asbestos, paper, or plastic, or a noncontinuous strand such as staple, and the like. An "end" is one or a contiguous group of such strands of yarn. The term "RMS," which is an abbreviation of root-mean-square, is an arbitrary measurement of surface texture and is described in detail in the publication, Surface Texture (ASA B 46.1-1962), The American Society of Mechanical Engineers, United Engineering Center, 345 East 47th Street, New York 17, N.Y., page 16 (1962).
The invention is applicable to many phases of yarn handling, the particular use disclosed herein being merely illustrative and not limiting thereof.
Aspirators are often used in the melt-spin process subsequent to the extrusion and quench stages. An aspirator generally comprises inlet and outlet ends connected by a passageway to which a source of air under pressure is connected via an orifice or orifices. This air is introduced into the aspirator passageway to create an atmosphere productive of suction therethrough. By placing the aspirator sufficiently near the path of the yarn, operation of the aspirator will cause the yarn end or ends to pass therethrough to a collection receptacle. In multiple end spinning, a break in one of the yarn ends is detected by a sensing device which automatically triggers an aspirator located in close proximity to the running yarn ends. The yarn ends are then aspirated to waste at a collection receptacle to prevent the yarn from snarling or hanging up. Thereafter, the operator can cut the yarn ends at the aspirator inlet and proceed to string-up again. Due to equipment configuration or the dictates of the particular string-up device, it may be preferable to string-up only one yarn end at a time. If so, the aspirator provides a temporary means for maintaining any other yarn ends out of the way until the operator can string them up. Aspirators are also utilized in single end spinning, one application being that of a temporary collecting device during the windup stage when starting a new package.
With respect to any of the aforementioned applications, high velocity air is introduced into the aspirator passageway through an orifice or orifices to create the desired suction effect. As a consequence, noise is produced inside the aspirator at and downstream of the orifice(s). The sound waves thus generated are then propagated through the inlet and outlet ends of the aspirator. The operator is confronted primarily with the noise issuing from the inlet end of the aspirator as the noise traveling through the outlet end passes, along with the aspirated yarn, through exhaust pipes to a collection point which is shielded from the operator. The noise emitted, as measured 6 inches in front of the aspirator inlet end with an air supply line pressure ranging from 40 to 90 psig, has been found to exceed 100 dB(A) in some instances. The frequency component of the aspirator noise is situated in the high frequency levels, i.e., greater than 2,000 cycles per second, which has been shown to be more harmful than the low frequency levels.
Although the aspirator as described in the aforementioned situations is an intermittent source of noise, it could be a continuous noise source. In either event, as a major contributor of noise or as a minor component in a process which has several other sources of noise, it is desirable to bring the noise level down to tolerable limits.
There are several approaches to noise reduction in a work environment. One is the use of hearing protection devices such as helmets, ear plugs, or ear muffs by the operator exposed to the noise. The protection afforded, however, relates directly to proper use and maintenance of the devices. The difficulty, from a managerial viewpoint, lies in getting the operator to use these protective devices. To avoid this problem, applicants have provided a muffler which reduces the noise emitted at the inlet end of the aspirator by up to 22.5 .DELTA. dB(A) and which thereby brings the noise to within acceptable levels.
The introduction of a muffler, however, presents another problem. The muffler of the present invention is adapted to fit over the inlet end of the aspirator. By being mounted in such a manner, it acts as a restrictor, resulting in decreased suction and a loss in yarn tension. Rather than design a more efficient aspirator, applicants have found that by finishing the muffler inlet end with a high RMS surface, there is a gain in yarn tension which compensates for the yarn tension loss produced by coupling the muffler of the present invention with the aspirator.